Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.29   10.263%   $269.3615   $269.36   $269.35   $269.40  
  Purchase #2 $54.31   7.362%   $58.3083   $58.31   $58.30   $58.30  
  Purchase #3 $159.40   10.684%   $176.4303   $176.43   $176.45   $176.40  
  Purchase #4 $20.31   3.649%   $21.0511   $21.05   $21.05   $21.10  
  Purchase #5 $236.97   6.565%   $252.5271   $252.53   $252.55   $252.50  
  Purchase #6 $89.40   10.495%   $98.7825   $98.78   $98.80   $98.80  
  Purchase #7 $95.46   10.551%   $105.532   $105.53   $105.55   $105.50  
  7 purchase totals = $900.14       $981.9928   $981.99   $982.05   $982.00